Image Capturing Apparatus, Imaging Circuit, and Image Capturing Method

1. An image capturing apparatus for capturing an image with solid state imaging devices, the image capturing apparatus comprising: a compressing section for compressing digitalized data of an image captured with the solid state imaging devices; a memory for temporarily storing the compressed image data that is compressed by the compressing section; a decompressing section for decompressing the compressed image data that is read out from the memory; and a signal processing section for performing an image quality correction operation on the image data decompressed by the decompressing section, wherein the compressing section generates the compressed image data that contains (i) a maximum value and a minimum value of pixel data in a block constituted by the pixel data from a predetermined number of pixels; (ii) information regarding positions where the maximum value and the minimum value are located in the block; and (iii) quantized data obtained by subtracting the minimum value from each pixel data value of the block, except for the pixel data values of the block corresponding to the maximum value and the minimum value in the block, and then quantizing the results of the subtraction, wherein the quantized data for the block corresponds to a number of pixels equal to two pixels less than the predetermined number of pixels.

2. The apparatus according to claim 1 , wherein the compressing section includes a maximum/minimum value detecting unit for detecting, for each block, the maximum value and the minimum value of the pixel data and the information regarding the positions of the maximum value and the minimum value in the block, a quantizing unit for quantizing the results of subtracting the minimum value in the block from each pixel data value in the block according to a dynamic range calculated as a difference between the maximum value and the minimum value in the block, and a packing unit for packing, for each block, the maximum value and the minimum value in the block, the information regarding the positions of the maximum value and the minimum value, and the quantized data except for those corresponding to the maximum value and the minimum value among the data quantized by the quantizing unit so as to generate compressed image data.

3. The apparatus according to claim 2 , wherein a quantization word length employed in the quantizing unit is a fixed value.

4. The apparatus according to claim 2 , wherein the compressing section further includes a pre-compressing unit for supplying, after converting a gradation of the digitalized image data according to luminosity characteristics of the human eye and decreasing the number of bits of the gradation-converted image data, the image data to the compressing section.

5. The apparatus according to claim 2 , wherein the quantizing unit employs a quantization step size of a power of two and quantizes the results of the subtraction with a bit shifter that shifts data to the right by a number of bits corresponding to the dynamic range.

6. The apparatus according to claim 5 , wherein the packing unit packs a shift amount employed by the bit shifter instead of the maximum value in the block.

7. The apparatus according to claim 2 , wherein the decompressing section includes a dequantizing unit for dequantizing the quantized data extracted from the compressed image data for each block according to the dynamic range calculated as a difference between the maximum and minimum values extracted from the compressed image data, an adding unit for adding the minimum value to the data dequantized by the dequantizing unit, and an output controlling unit for outputting the maximum value, the minimum value, and the values output from the adding unit in the order that the values of the original pixel data have been input to the compressing section on the basis of the information regarding the positions of the minimum and maximum values that is extracted from the compressed image data for each block.

8. The apparatus according to claim 7 , wherein the compressing section further includes a pre-compressing unit for supplying, after converting a gradation of the digitalized image data according to luminosity characteristics of the human eye and decreasing the number of bits of the gradation-converted image data, the image data to the compressing section, and wherein the decompressing section further includes a post-decompressing unit for decompressing the image data output from the output controlling unit in a procedure opposite to that employed by the pre-compressing unit.

9. The apparatus according to claim 7 , wherein the quantizing unit of the compressing section employs a quantization step size of a power of two and quantizes the results of the subtraction with a bit shifter that shifts data to the right by a number of bits corresponding to the dynamic range, and wherein the dequantizing unit of the decompressing section dequantizes the quantized data extracted from the compressed image data with a bit shifter that shifts data to the left by a number of bits corresponding to the dynamic range.

10. The apparatus according to claim 1 , wherein the block is constituted by the pixel data of the same color component.

11. The apparatus according to claim 1 , wherein the block is constituted by the pixel data contained in a rectangular area on a captured image.

12. The apparatus according to claim 1 , wherein the decompressing section and the signal processing section are connected to the memory through a common bus, and wherein the image data decompressed by the decompressing section is supplied to the signal processing section directly and not through the bus.

13. The apparatus according to claim 12 , wherein the compressing section writes the compressed image data in the memory through the bus.

14. The apparatus according to claim 1 , wherein the compressing section is formed on the same chip as a circuit for performing digitalizing of the image data.

15. The apparatus according to claim 14 , wherein the compressing section is formed on the same chip as the solid state imaging devices as well as the circuit for performing digitalizing of the image data.

16. The apparatus according to claim 14 , wherein a function of the compressing section is controlled to be turned on and off by an external control circuit.

17. An imaging circuit used for capturing an image, the imaging circuit comprising: solid state imaging devices each for converting an incident light into an electric signal; a digitalizing circuit for digitalizing the imaging signals generated by the solid state imaging devices; and a compressing circuit for compressing an image signal supplied from the digitalizing circuit, wherein the solid state imaging devices, the digitalizing circuit, and the compressing circuit are formed on the same chip, and wherein the compressing circuit includes a maximum/minimum value detecting circuit for detecting, for each block constituted by pixel data of a predetermined number of pixels, a maximum value and a minimum value of the pixel data and information regarding positions where the maximum value and the minimum value are located in the block, a quantizing circuit for quantizing results of subtracting the minimum value in the block from each pixel data value in the block according to a dynamic range calculated as a difference between the maximum value and the minimum value in the block, so as to generate quantized data, and a packing circuit for packing, for each block, (i) the maximum value and the minimum value in the block; (ii) the information regarding the positions of the maximum value and the minimum value; and (iii) the quantized data except for those data of the quantized data corresponding to the maximum value and the minimum value among the data of the block quantized by the quantizing circuit, wherein the quantized data that is packed for the block corresponds to a number of pixels equal to two pixels less than the predetermined number of pixels, so as to generate compressed image data.

18. An image capturing method for capturing an image with solid state imaging devices, the method comprising: causing a compressing section to generate compressed image data that contains (i) a maximum value and a minimum value of pixel data in a block constituted by pixel data from a predetermined number of pixels, (iii) information regarding positions where the maximum value and the minimum value are located in the block, and (iii) quantized data obtained by subtracting the minimum value from each pixel data value of the block, except for the pixel data values of the block corresponding to the maximum value and the minimum value in the block, and then quantizing the results of the subtraction on the basis of digitalized data of an image captured with the solid state imaging devices, wherein the quantized data for the block corresponds to a number of pixels equal to two pixels less than the predetermined number of pixels, and to temporarily store the compressed image data in a memory; causing a decompressing section to read out the compressed image data stored in the memory and to decompress the compressed image data; and causing a signal processing section to perform an image quality correction operation on the image data decompressed by the decompressing section.